A number of features in existing telecommunications facilitate intrusion by one party into a call (or session) between two other parties. Whisper page, for example, allows subscribers to communicate with a busy extension without interrupting a call in progress. When a busy station is called using the whisper page feature, the busy station user will hear the voice announcement and/or tones through the handset receiver. The station using the whisper page can choose to communicate with the calling station by pressing a key, such as the [*] key. Neither the voice of the station sending the whisper page nor the busy station's response is audible to the outside party. Barge-in allows a subscriber to enter an existing conversation without the other party knowing about the conversation. A warning tone is sent to inform the party that a three-way conference has been established. A call waiting feature causes a busy station to emit an audible set of tones to notify the user of an incoming call. The user can place the current call on hold to answer the incoming call. In a multi-party conference call, party entry and exit tones are broadcast over the various bearer channels to the call.
As can be seen from the above, the features can disrupt the call in progress. The disruption ranges from the injection of an audible tone to the complete disruption of the call. Such intrusions act immediately regardless of whether the parties to the intruded call are in mid-sentence. Intrusions can therefore cause misunderstandings, delay the duration of the call, and annoy participants.